Magnetic Random Access Memory (xe2x80x9cMRAMxe2x80x9d) is a non-volatile memory that may be suitable for long term data storage. MRAM devices may perform read and write operations faster than conventional long term storage devices such as hard drives. In addition, MRAM devices may be more compact and may consume less power than conventional storage devices.
A typical MRAM device may include an array of memory cells where word lines extend along rows of the memory cells and bit lines extend along columns of the memory cells. Each memory cell may be located at a cross point of a word line and a bit line.
A memory cell in an MRAM device stores a bit of information according to an orientation of a magnetization. The magnetization of a memory cell assumes one of two stable orientations at a given time. These two orientations are known as parallel and anti-parallel and represent logic level values of xe2x80x980xe2x80x99 and xe2x80x981xe2x80x99, respectively.
The magnetization orientation affects the resistance of a memory cell such as a spin dependent tunneling junction device. For instance, the resistance of a memory cell is a first value R if the magnetization orientation is parallel, the resistance of the memory cell is increased to a second value (R+xcex94R) if the magnetization orientation changed from parallel to anti-parallel. The magnetization orientation of a selected memory cell, and therefore the logic state of the memory cell, may be read by determining the resistance state of the selected memory cell.
One of the challenges with MRAM devices involves electrically isolating the circuits that comprise the memory cells while maintaining a sufficient level of packing density. Although additional components such as transistors may be used to increase the isolation of memory cells, an increase in the number of components typically results in a decrease in the packing density of the memory cells, i.e., the number of memory cells per a given area, and a decrease in the packing density generally results in increased costs. It would be desirable to be able to increase packing densities while increasing the electrical isolation of memory cells and while improving the read performance of the MRAM memory.
In one exemplary embodiment, the present disclosure provides a method of performing a read operation from a first memory cell in a memory cell string that includes the first memory cell coupled to a second memory cell. The method includes providing a voltage to a first end of the first memory cell string that is closest to the first memory cell, providing a ground source to a second end of the first memory cell string that is opposite the first end, and determining whether a voltage change occurred at a node between the first and second memory cells in response to writing the first memory cell to a first state.